Tuesday’s event was part of the Semana Nautica summer sports festival.
Clark, 50, a multi-time winner of the biathlon, covered the 1k swim and 5k run in 38 minutes, 56 seconds. His swim time of 14:36 was the fastest of the evening.
The top woman duathalon finisher was Whitney Bruice (7th overall) in 47:00.
The 5k run was won by Scott Engelman in 21:56, with Kristi Miller taking top honors for women (third overall) in 26:45.
In the mile swim, Felipe Rivera took top honors in 18:52 followed by Ed Smith (19:06) and Greg Gaitan (19:11). The top woman was triathlete Lauren Capone in 21:07.
The Semana Nautica Biathlon is on Saturday at 9 a.m. at East Beach.